There is no doubt that the advent of immunocytochemical techniques, by enhancing our ability to detect specific cell products or markers, has opened new avenues in the understanding of human diseases, and in our ability to perform better diagnosis in surgical pathology. The rapid development of this field has resulted in thousands of publications in the literature regarding immunocytochemistry in diagnostic pathology. This explosion of knowledge makes necessary publications summarizing what are the main markers available and how they can be used in the diagnosis of tumors. The need of a more organized and structured knowledge was evident during the workshop in Immunocytochemistry of Tumor Diagnosis that took place in the City of Detroit an October 1984. This book is the result of that workshop in which 22 chapters are focusing an the main subject of differential diagnosis of tumors. Jose Russo, M.D. Editor xiii ACKNOWLEDGEMENTS I wish to thank my many associates at the Michigan Cancer Foundation for their help in the preparation of this manuscript. I give thanks to Dr.